1. Field of the Invention
This invention relates to test equipment for electrically testing parts used in the assembly of hybrid integrated circuit apparatus, and, more specifically, this invention relates to the alignment of the probe testing apparatus relative to the devices to be tested by manipulating a separate theta stage, a separate X-Y stage, and a separate Z stage.
2. Description of the Prior Art
To align a probe station which includes electrical test leads to hybrid integrated circuit elements requires the movement of three stages, an X-Y stage, a theta or rotary stage, and a vertical stage. The elements to be tested are oriented by X-Y movement, and then they are rotated by a theta stage, which is a rotary displacement of the X-Y stage about a fixed point. After the X-Y and theta stages have been aligned, a test ring, which includes test leads or probes, is moved vertically downwardly in a Z stage movement to cause the electrical test probes to contact the desired portions of the integrated circuitry being tested.
Because the integrated circuitry being tested is so very small in relation to the ability of a human tester to both see and control his hand movements, the integrated circuitry to be tested is usually enlarged optically, as by a magnifying glass, and the alignment of the test probe apparatus is done by visual reference to the circuitry to be tested. The X-Y stage and the theta (rotary) stage are typically tied together, so that coordinated X-Y and theta movements are made. A single index location or mark is normally indexed first, by X-Y movement of a so-called "joystick", by which relatively "large" movements of the human tester on the joystick are reduced substantially by a simple pivoted lever. Since the two stages are tied together, an X-Y movement for alignment is followed by a theta or rotary movement, but the rotary movement causes some displacement of the X-Y stage. Accordingly, the X-Y stage is then aligned again, which results in rotary displacement, so that another theta stage movement is required. However, it may be understood that successive movements are substantially diminished so that ultimately the circuit elements are properly indexed for testing.
When the integrated circuit chip has been appropriately aligned under the two index markers, the electrical contact between the various portions or paths on the chip to be tested is accomplished by movement vertically downwardly of a fixed ring which includes a plurality of discrete test leads that are pre-positioned for each particular integrated circuit chip to be tested. Obviously, the probe test ring is appropriately indexed before the testing begins for each particular chip. When the chip is in position for test, the probe ring, with the electrical leads, is moved downwardly to make electrical contact. Through appropriate test equipment, the various components or circuits on the integrated circuit chip are then electrically tested. At the conclusion of the test, the probe ring is raised, the chip which has been tested is moved, and another chip is aligned for appropriate testing.
Depending on the skill of the human tester, a substantial amount of time is required for the alignment of each discrete chip to be tested. Since time is of the essence, any time which is saved in the alignment process is time gained in the overall testing sequence.
Movement of the Z stage downwardly for testing and upwardly after testing is generally not a problem with respect to time. However, movement of the X-Y stage and the theta stage is where the time consuming operation takes place, and it is at this portion of the testing that the substantial improvements may be affected. In the prior art, the X-Y stage and the theta stage are generally tied together so that double movement has to be made to keep the X-Y stage in proper alignment as the theta stage is moved. This results in the human tester being required to maintain a constant alignment by continuous movements altering the alignment procedure.
In the apparatus of the present invention, the problem of continuous alignment movements is obviated by separating or divorcing the theta stage from the X-Y stage. With the theta stage fixed in place for only rotary movement, movement is required only of the X-Y stage in order to align the primary alignment index mark to a location over the center of rotation of the theta stage. This is accomplished manually. Rotation of the theta stage then results in the alignment of the secondary index mark for complete alignment of a chip.